Myster Science

In its simplest form, the Big Bang theory assumes that matter and radiation are uniformly distributed throughout the universe and that general relativity is universally valid. While this can account for the existence of the cosmic microwave background radiation and explain the origin of the light elements, it does not explain the existence of galaxies and large-scale structure. The solution of the structure problem must be built into the framework of the Big Bang theory.

While there is no authoritative model for how the universe was formed, but scientists have agreed on a most popular model. The most popular theory is called the nebular hypothesis. It did fall out of favor for a number of years, but now it is back as the definitive model. According to the nebular hypothesis, our Solar System began around 4.6 billion years ago when part of a molecular cloud of interstellar gas, which was filled with particles of ice, dust, rock, and other particles, collapsed. These clouds collapsed from some kind of turbulence that caused it to heat up and eventually turn into a star. Most of the cloud formed the Sun. Other material from the cloud flattened around the Sun forming a planetary disc. The material from the planetary disc, also known as the solar nebula, went to form the planets and other objects in our Solar System. Some of the material forms a solid object, which gets larger as other particles collide with it and stick together. Eventually, the object gets large enough to attract more dust and ice with its gravitational influence. These balls then form the cores of the planets. If one of these balls leaves the Sun early enough, it turns into a comet. Because of radiation and collision with other objects, these balls of ice, rock, and dust turned into very different planets. Astronomers believe that it took millions of years for the planets to form. Asteroids and other planetesimals are “failed planets” – objects formed from the solar nebula that never got large enough to turn into planets. Currently, astronomers are studying planets forming in other Solar Systems.